Application of the off-gas method to the measurement of oxygen transfer in biofilters

To determine the oxygen mass transfer in clean water in biofilters, a method based on the follow up of the oxygen fraction in the off gas during the oxidation ofsulphite in excess has been evaluated and applied to a pilot-scale unit (250 L, superficial gas velocity from 0 to 5.6×10−3 mN s−1, superficial liquid velocity from 0 to 2.5×10−3 ms−1). Tests performed on a two-phase reactor showed that, without any cobalt addition, standard oxygen transfer efficiencies (SOTE) obtained from the proposed method are not statistically different from those issued from the standardised method. A relationship has been proposed to express SOTE values as a function of the conductivity, and the influence ofthe gas and liquid velocities on SOTE and kLa has been investigated.